1. Field of the Invention
The present invention concerns a method for sealing the space between an interior lining and a borehole, an exterior casing or an exterior cylindrical pipeline in which it is accommodated.
2. Description of the Prior Art
It is more particularly concerned with a method for use with a lining formed from a tubular preform with a flexible and radially deformable wall, hardenable in situ, the preform being adapted to occupy a first or contracted state in which its greatest transverse dimension is substantially less than the inside diameter of the borehole, the casing or the pipeline and a second or expanded state in which its outside surface has a cylindrical shape the diameter of which is substantially equal to the inside diameter of the borehole, the casing or the pipeline, the preform being hardened when it is in the expanded state inside the borehole, the casing or the pipeline to form a rigid lining therein.
A preform of this kind and the method of installing it are described in the following documents, among others: WO-A-91 18180, FR-A-2 703 102 and FR-A-2 704 898.
A lining of this type is particularly suitable for repairing oil well casings or a damaged (for example perforated) section of the wall of a pipeline such as a gas pipeline or an oil pipeline.
To this end the contracted preform is inserted into the casing or the pipeline and moved up to the area to be repaired, where it is fitted and then expanded into intimate contact with the surface of the inside wall of the casing or the pipeline, after which it is hardened.
The wall of the preform is usually made from a thermosetting resin reinforced with fibers and hardened is achieved by heating (by the Joule effect or by means of a hot liquid introduced into the preform).
This method is satisfactory.
However, there is not always a good seal between the lining and the borehole, the casing or the pipeline around it.
In some cases liquids or gases in the soil can pass through perforations or other openings in the wall of the borehole, casing or pipeline, finding their way into the annular space between the lining and the borehole, casing or pipeline, and eventually flowing into the interior of the latter.
The pressure of the liquid or the gas in this annular space, even if it has a size on the micrometer scale, firstly causes the lining to contract and secondly causes the borehole, casing or pipeline to expand, so increasing the size of said annular space and degrading the seal.
To our knowledge there is no simple method of achieving a good seal at this location.
An object of the present invention is to propose such a method.